CriticalCVE-2021-30952

    Apple Multiple Products Integer Overflow or Wraparound Vulnerability (CVE-2021-30952)

    Published In CISA KEV since Sources: Debian, CVE.org, Red Hat

    What is affected, what to do

    An integer overflow was addressed with improved input validation. This issue is fixed in tvOS 15.2, macOS Monterey 12.1, Safari 15.2, iOS 15.2 and iPadOS 15.2, watchOS 8.3.

    The vulnerability is being actively exploited; treat it as a priority. Update Apple watchOS to version 8.3, Apple iOS and iPadOS to version 15.2, Apple macOS to version 12.1. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Apple watchOS lt *..8.3
    • Apple iOS and iPadOS lt *..15.2
    • Apple macOS lt *..12.1
    • Apple macOS lt *..15.2
    Fixed in
    • Apple watchOS 8.3
    • Apple iOS and iPadOS 15.2
    • Apple macOS 12.1
    • Apple macOS 15.2

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    8.8

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v3

    7.8

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: Debian, CVE.org, Red Hat

    7.0 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 94.1

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    209.88 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploited
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    8.8 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    7.8
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    7.0 %
    Moderate — model estimates 1-10% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    94.1
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    CISA assessment (SSVC)
    Exploitation: active · not automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 5 March 2026
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-190

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This is a WebKit memory-corruption bug: loading a crafted web page with minimal user interaction is enough for code execution, and no authentication is required. Bugs like this usually serve as the initial stage of exploit chains delivered through watering-hole sites, malvertising or targeted links. Typical targets are high-value individuals such as executives, journalists and staff in critical-infrastructure roles. CISA does not flag ransomware use, but exploitation likelihood is still rated high. The fix has been available since late 2021, so real exposure sits almost entirely in unpatched legacy devices and BYOD. Organisations with a fully managed, current Apple fleet need only a verification report. Any still-vulnerable device with access to corporate data warrants immediate, high-priority handling.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Build the inventory: Pull every Apple endpoint with OS and Safari version from your MDM (Jamf, Intune, Kandji, Workspace ONE). Vulnerable devices are anything below iOS/iPadOS 15.2, macOS Monterey 12.1, Safari 15.2 (on Big Sur/Catalina), tvOS 15.2 or watchOS 8.3.
      • Force the update: The fix shipped in tvOS 15.2, macOS Monterey 12.1, Safari 15.2, iOS/iPadOS 15.2 and watchOS 8.3. Supported hardware should already be well past these releases, so in practice you push the latest available version via MDM update commands or Declarative Device Management with an enforced deadline.
      • Isolate legacy hardware: Pull devices that cannot receive 15.2/12.1 (older iPhones/iPads, pre-Monterey Macs without the Safari update) off corporate Wi-Fi, VPN and SSO immediately. Check the vendor advisory to see whether Apple backported a fix to older release trains.
      • Don't rely on switching browsers on iOS/iPadOS: Chrome, Edge and Firefox on iOS all render with WebKit and are equally exposed. On macOS, any app embedding WKWebView (Mail, in-app browsers) stays exposed until the OS or Safari is patched.
      • Preserve suspect devices: For outdated devices showing signs of compromise, capture a sysdiagnose and an iOS backup for forensic triage (e.g. Mobile Verification Toolkit) before wiping. Then revoke all credentials and session tokens stored on the device (M365, SSO, VPN certificates).

    2. Runbook step 2

      Mitigation layers

      • Access control (Conditional Access/NAC): Set an Intune/Entra compliance policy with a minimum OS version (at least 15.2/12.1, ideally the current supported line). Block non-compliant devices from mail, SharePoint, VPN and internal web apps. Use 802.1X NAC to drop legacy devices into a quarantine VLAN with no internet breakout.
      • Web proxy/SWG: Block outdated WebKit user agents or redirect them to a notice page, e.g. CPU (iPhone )?OS 1[0-4]_, CPU (iPhone )?OS 15_[01][ _], Version/1[0-4]\.\d.*Safari or Version/15\.[01] .*Safari. Deny uncategorised and newly registered domains for this device class.
      • DNS filtering: Enforce protective DNS on mobile devices off-network as well, via an MDM DNS-over-HTTPS profile, so exploit landing pages and malvertising domains don't resolve.
      • Endpoint hardening: On supervised devices that temporarily cannot be updated, use the MDM restriction to disable JavaScript in Safari and block unmanaged app installs. On patched devices for high-risk users (executives, admins, frequent travellers), also enable Lockdown Mode. It requires iOS 16/macOS Ventura or later.
      • Process: Define a binding update SLA (e.g. 7 days for WebKit security updates) and retire end-of-support hardware per ISO 27001 A.8.1 (user endpoint devices). Exceptions must be documented and approved by security with an expiry date.

    3. Runbook step 3

      Detection rules

      • MDM/inventory query as baseline detection: Run a daily report of devices with OSVersion < 15.2 (iOS/iPadOS/tvOS), < 12.1 (macOS without Safari ≥ 15.2) or < 8.3 (watchOS). Each hit becomes a ticket assigned to the device owner.
      • macOS EDR process ancestry: Unusual child processes of WebKit renderer processes are a strong indicator. KQL (Defender for Endpoint): DeviceProcessEvents | where InitiatingProcessFileName has "com.apple.WebKit.WebContent" and FileName in~ ("sh","bash","zsh","osascript","curl","python3","perl"). Sigma shape: logsource: product=macos, category=process_creation, ParentImage|contains: 'WebKit.WebContent'.
      • Crash telemetry: Clusters of com.apple.WebKit.WebContent crash reports with EXC_BAD_ACCESS/KERN_INVALID_ADDRESS point to failed exploitation attempts. Sources are ~/Library/Logs/DiagnosticReports/*.ips on macOS and the analytics data in a sysdiagnose on iOS.
      • Proxy logs: Find outdated WebKit user agents and correlate them with visits to rare domains. Example SPL: index=proxy http_user_agent="*OS 15_1*" OR http_user_agent="*Version/15.1*Safari*" | stats dc(dest_domain) values(dest_domain) by src_ip, user.
      • Network telemetry (Zeek/Suricata): Treat connections from mobile subnets to newly registered domains as a possible post-exploitation payload download when they are followed by unusual outbound TLS (new JA3/JA4 fingerprints, periodic beaconing).

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    An integer overflow was addressed with improved input validation. This issue is fixed in tvOS 15.2, macOS Monterey 12.1, Safari 15.2, iOS 15.2 and iPadOS 15.2, watchOS 8.3. Processing maliciously crafted web content may lead to arbitrary code execution.

    Source: Debian Security Advisories, NVD (NIST), cvelistv5, CISA KEV Catalog, CVE.org (MITRE), redhat_csaf

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    AppleiOS and iPadOS
    • < 15.2
    • 15.2
    ApplemacOS
    • < 12.1
    • < 15.2
    • 12.1
    • 15.2
    ApplewatchOS
    • < 8.3
    • 8.3
    applesafari
    • < 15.2
    • 15.2
    webkitgtkwebkitgtk
    • < 2.34.4
    • 2.34.4
    wpewebkitwpe_webkit
    • < 2.34.4
    • 2.34.4

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebiandebian_linux10.0
    Linuxdebiandebian_linux11.0
    Linuxdebianwebkit2gtkbullseye
    Linuxdebianwebkit2gtkbuster
    Linuxdebianwpewebkitbullseye
    macOSapplemacos—
    Mobileappleiphone_os—
    Otherfedoraprojectfedora34
    Otherfedoraprojectfedora35
    Otherappleipados—
    Otherappletvos—
    Otherapplewatchos—

    Weakness classes (CWE)

    • CWE-190Integer Overflow or Wraparound

      Base

      The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.

      Entry at MITRE CWE-190

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited

    References & sources

    • support.apple.comen-us/HT212975x_refsource_MISC, Release notes, Vendor advisory
    • support.apple.comen-us/HT212976x_refsource_MISC, Release notes, Vendor advisory
    • support.apple.comen-us/HT212978x_refsource_MISC, Release notes, Vendor advisory
    • support.apple.comen-us/HT212980x_refsource_MISC, Release notes, Vendor advisory
    • support.apple.comen-us/HT212982x_refsource_MISC, Release notes, Vendor advisory
    • openwall.com[oss-security] 20220121 WebKitGTK and WPE WebKit Security Advisory WSA-2022-0001Mailing list, x_refsource_MLIST, Mailing list, Third-party advisory
    • lists.fedoraproject.orgFEDORA-2022-25a98f5d55Vendor advisory, x_refsource_FEDORA, Broken link
    • debian.orgDSA-5061Vendor advisory, x_refsource_DEBIAN, Mailing list, Third-party advisory
    • debian.orgDSA-5060Vendor advisory, x_refsource_DEBIAN, Mailing list, Third-party advisory
    • lists.fedoraproject.orgFEDORA-2022-f7366e60cbVendor advisory, x_refsource_FEDORA, Broken link
    • cloud.google.comblog/topics/threat-intelligence/coruna-powerful-ios-exploit-kitThird-party advisory, Exploit, Third-party advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2021-30952government-resource, US government resource
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